This application relates generally to gas turbine engines and, more particularly, to guide vane assemblies for gas turbine engines.
At least some known aircraft gas turbine engines include a compressor, a combustor, a turbine, and an augmentor or “afterburner”. Airflow entering the compressor is compressed and directed to the combustor where it is mixed with fuel and ignited, producing hot combustion gases used to drive the turbine. As the performance demands of aircraft have increased, performance demands of the engines have also increased. Initially augmentors or “afterburners” were added to improve thrust. As range demands increased, low pressure rotors were added providing higher mass flow resulting in increased thrust at better specific fuel consumption. This demand for increased thrust prevailed with adding augmentation, “afterburning” to the bypass air. Additionally, mission demands increased for multi-role weapon systems. For example, engines are being designed to transition between conventional take-off and landing (CTOL) operations, as well as, short-takeoff and vertical landing (STOVL) operations. Augmentors are used in gas turbine engines to increase thrust as needed in a flight envelope and are located downstream from the turbomachinery. Additional thrust is produced within the augmentor when oxygen contained within both the core gas flow and the bypass air of the engine is mixed with fuel and burned. An exemplary afterburning turbofan engine provides provisions to burn the core gases and fan air sequentially. These applications provide the highest level of specific thrust as they consume the highest percentage of oxygen including the majority of the bypass air including that which is used for cooling.
At least one known engine augmentor includes a plurality of radial fuel spray bars and a combination of radial and circumferential flame holders, e.g. V-gutters, that are positioned directly in the core gas path to deliver the fuel in an circumferentially and radially distributed manner and to maintain the flame once ignited. An advantage of the radial fuel spray bars is that it is possible to evenly distribute fuel about the annulus of the augmentor at any particular radial and circumferential position. The combination of radial spraybars with their circumferential spacing with radially distributed holes allows for fine tuning of the required fuel air distribution. Mechanical flame holders are configured to act as aerodynamic bluff bodies, thus creating a low velocity wake within an area downstream. However, modern gas turbine engines are generally designed to operate at an increased through mass flow ratio. Accordingly, augmentors that include bluff bodies may have a reduced stability which limits the operability flight map, and also limits the engine/augmentor envelope. This limit is established by the basic stability characteristic of the bluff body.